It’s often the case that trends hailed as the next big thing are actually age-old practices which have made their way to the mainstream. There are few better examples than fermentation, which has become wildly popular in recent years, but which has a history that stretches back, in essence, to the beginning of human existence (historians have found signs of food and drink fermentation as early as 7,000BC). From chocolate to charcuterie, many of our favourite foods are created as a result of fermentation, which, taken from the Latin verb ‘fervere’, meaning to boil, is basically the process of breaking down starch and sugar by bacteria and yeast. Its purpose may once have been to preserve food, but today fermentation is all about adding flavour – and it is not just a preserve of innovative chefs, with the likes of kimchi, kefir and sauerkraut lining supermarket shelves.

So how does it work? In a nutshell, there are three main fermentation methods – lactic acid (which makes the likes of sauerkraut, kimchi and yoghurt), alcoholic (responsible for beer and wine) and acetic (which produces vinegar, creating the likes of kombucha and apple cider vinegar). For many cooks, their fermentation gateway is raw vegetables, which just require salt, a vessel and time to ferment. In sauerkraut, for example, adding salt to cabbage and sealing it keeps out oxygen, and stops harmful bacteria from multiplying and spoiling the cabbage. Good bacteria, though, eats the sugars and starches in the cabbage, producing lactic acid and creating a sour flavour, vitamins and probiotics and a long preservation time. We might be hard-wired to mistrust food that’s been left out, but the anaerobic environment means that, once the mixture reaches a certain pH, bad bacteria can’t survive.

In restaurant kitchens, this sort of basic fermentation is now standard, with chefs finding new, innovative ways to weave ferments in their menus, from fermented fruits to garums (a fermented fish sauce nicknamed 'Roman ketchup' thanks to its ample use in Ancient Rome). Among them is Ramael Scully, whose restaurant Scully St James’s in London is lined with jars of fermented, pickled and dehydrated produce and is home to a downstairs kitchen which has become a makeshift fermentation laboratory, complete with dehydrators, incubators and rice cookers. ‘For a lot of people fermentation is a massive word,’ he says,’ but it’s been going on for donkey’s years and at its heart is simple.’ As well as tapping into waste reduction and health movements (the vitamins, prebiotics and probiotics in ferments are said to reduce heart disease, help digestion and boost our immune systems), Scully, as he is best-known, says the fermentation craze has been helped along by Noma co-founder and chef René Redzepi and its former fermentation lab head David Zilber, who released The Noma Guide To Fermentation book and, in doing so, introduced plenty of cooks – both professional and home – to the technique.

With a process that has so many possibilities, it can be difficult to know where to begin, but Scully says there isn’t a fixed guide when it comes to fermenting. It is, though, crucial to learn the basics. ‘Always work in a clean environment, and sterilise, sterilise, sterilise,’ he says. While some people run the jars they use through their dishwasher, you can also steam them or cover them with boiling water and dry them in an oven at around 150C. Make sure to stool ferments in a cool, dark place, out of direct sunlight, and ‘burp’ your jars to release air, and pressure, every few days. ‘From there, there are no rules,’ Scully says. ‘It’s about how funky you want it and what it is you want to ferment, there’s no one way to do it. But be prepared to make mistakes.’ And don’t assume you know how the end product will taste – slight tweaks to the process can enormously alter an ingredient’s flavour profile, so it's important to research the right salt ratios. ‘Salt and bitterness creates sweetness in time,’ he says, sagely. ‘Think of why Moroccans have preserved lemons – salt and the bitterness in lemons creates a fragrant sweetness.’